The generation of three-dimensional video is realized by the use of the human physiological functions of perception. That is, observers perceive three-dimensional objects in the course of the comprehensive processing in their brains based on the perception of a displacement of images respectively entering their right and left eyes (binocular parallax) and the perception with the angle of convergence, the perception with the physiological function that occurs when adjusting the focal length of crystalline lenses of the eyes using the ciliary body and the Zinn's zonule (the focal length adjustment function), and the perception of a change of image(s) seen when a motion is made (motion parallax). As a previous method of generating three-dimensional video utilizing the “binocular parallax” and the “angle of convergence” among the physiological functions of perception described above, there is a method of using glasses having different-colored right and left lenses to provide different images (parallax images) to right and left eyes, and a method of using goggles with a liquid crystal shutter to provide parallax images to right and left eyes by switching the liquid crystal shutter at a high speed, for example. There is also a method of representing three-dimensional images using a lenticular lens to allocate, to right and left eyes, images displayed on a two-dimensional display device respectively for the right and left eyes. Furthermore, similarly to such a method of using the lenticular lens, there is also a method developed for representing three-dimensional images by using a mask provided on the surface of a liquid crystal display to allow a right eye to view images for the right eye, and a left eye to view images for the left eye.
However, the methods of acquiring parallax images using the special glasses and goggles as described above are very annoying for the observers. On the other hand, with the method of using the lenticular lens, for example, it is necessary to divide the region of a single two-dimensional image display device into a region for the right eye and a region for the left eye. Therefore, such a method has an issue of being not appropriate for displaying images with high definition.
In consideration thereof, in recent years, the study has been made for a spatial image display device based on the light beam reproduction method (for example, see Non-Patent Literature 1). The light beam reproduction method is with the aim of representing spatial images by a large number of light beams irradiated from a display, and in theory, provides observers with precise information about motion parallax and information about focal length even with observation with naked eyes, so that the resulting spatial images are with the relatively low level of eye strain.